Evidence for Continental Drift Wegener (1915) proposed Pangaea – one large continent existed 200...
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Transcript of Evidence for Continental Drift Wegener (1915) proposed Pangaea – one large continent existed 200...
Evidence for Continental Evidence for Continental DriftDrift
Wegener (1915) Wegener (1915) proposed proposed PangaeaPangaea – – one large continent one large continent existed existed 200 million years ago200 million years ago
PanthalassaPanthalassa – one – one large oceanlarge ocean
Noted puzzle-like fit Noted puzzle-like fit of modern continentsof modern continents
Evidence for Continental Evidence for Continental DriftDrift
Matching Matching sequences of rocks sequences of rocks and mountain and mountain chainschains
Similar rocks on Similar rocks on different different continentscontinents
Evidence for Continental Evidence for Continental DriftDrift
Glacial ages and other Glacial ages and other climate evidenceclimate evidence
Evidence of glaciation Evidence of glaciation in now tropical regionsin now tropical regions
Direction of glacial flow Direction of glacial flow and rock scouringand rock scouring
Plant and animal fossils Plant and animal fossils indicate different indicate different climate than todayclimate than today
Evidence for Continental Evidence for Continental DriftDrift
Distribution of Distribution of organismsorganisms
Same fossils Same fossils found on found on continents that continents that today are widely today are widely separatedseparated
Modern Modern organisms with organisms with similar similar ancestriesancestries
Objections to Early Continental Drift Objections to Early Continental Drift ModelModel
Hostile criticism and open ridicule; Hostile criticism and open ridicule; Wegner was professional toastWegner was professional toast
Continents cannot plow through Continents cannot plow through ocean basinsocean basins
Tidal gravitational attractions too Tidal gravitational attractions too small to cause actual crustal small to cause actual crustal movementmovement
Evidence for Plate TectonicsEvidence for Plate Tectonics
• Earth’s magnetic field and Earth’s magnetic field and paleomagnetismpaleomagnetism
• Earth has magnetic polarityEarth has magnetic polarity
• North and South polaritiesNorth and South polarities
• Magnetic polarity recorded in igneous Magnetic polarity recorded in igneous rocksrocks– Magnetite in basaltMagnetite in basalt
Magnetic Polarity ReversalsMagnetic Polarity Reversals
Earth’s magnetic Earth’s magnetic polarity reverses polarity reverses periodicallyperiodically
Recorded in ancient Recorded in ancient rocksrocks
Paleomagnetism and the Paleomagnetism and the Ocean FloorOcean Floor
1955 – deep water rock mapping1955 – deep water rock mapping Magnetic anomalies Magnetic anomalies – regular pattern – regular pattern
of north-south magnetism “stripes”of north-south magnetism “stripes” Stripes were symmetrical about the Stripes were symmetrical about the
Mid Atlantic ridge suggesting that an Mid Atlantic ridge suggesting that an age sequence of the rocks was also age sequence of the rocks was also symmetricalsymmetrical
Sea Floor SpreadingSea Floor Spreading
Harry HessHarry Hess Depth recordings show sea floor Depth recordings show sea floor
featuresfeatures History of Ocean BasinsHistory of Ocean Basins
• Sea-floor spreadingSea-floor spreading• Mantle convection cells as driving Mantle convection cells as driving
mechanismmechanism
Plate Tectonic Processes: New Plate Tectonic Processes: New Rocks form at the spreading zoneRocks form at the spreading zone
Sea Floor Spreading EvidenceSea Floor Spreading Evidence Frederick Vine and Drummond Matthews Frederick Vine and Drummond Matthews
(1963) – everyone now believes in Wegner’s (1963) – everyone now believes in Wegner’s idea …idea …
Sea floor stripes record Earth’s magnetic Sea floor stripes record Earth’s magnetic polaritypolarity
Two halves of ocean floor are mirror imagesTwo halves of ocean floor are mirror images
Age of Ocean FloorAge of Ocean Floor
Late 1960s deep-sea drillingLate 1960s deep-sea drilling Radiometric dating of ocean rocksRadiometric dating of ocean rocks Symmetric pattern of age distribution about Symmetric pattern of age distribution about
mid-ocean ridgesmid-ocean ridges Oldest ocean floor only 180 million Oldest ocean floor only 180 million
years oldyears old